Scott Gration, who had led the US embassy in Nairobi since February last year, stepped down late last week, citing "differences with Washington regarding my leadership style".

It is understood that the State Department's inspector general is preparing to release a scathing report on Mr Gration, who is a close ally of President Barack Obama, following an extensive internal inquiry.

The former Air Force major general is said to have shown a "confrontational" and eccentric style of micromanagement that caused low morale and complaints among embassy staff.

Mr Gration repeatedly engaged in battles with employees and, according to a report by Foreign Policy, threatened at one point to "shoot them in the head" if they did not comply.

It is also alleged that Mr Gration might have lost his security clearance after the inquiry found he had used a personal email account for official business and set up an office in an embassy lavatory in order to get around the building's secure network.

Such was his eccentric style that soon after starting the job he also ordered that the heights of all embassy tables be adjusted and demanded that all clocks be recalibrated, according to reports.

The disclosures threaten to embarrass Mr Obama, who previously made Mr Gration his special envoy to Sudan after the veteran diplomat became an early champion of his presidential ambitions.

In his resignation statement last week, Mr Gration said: "I am very proud of my 35-year career of dedicated and honourable service to our great nation, leading at all times with integrity first and the highest ethical standards".

Mr Gration did not respond to an email requesting comment on the new allegations. A State Department spokesman did not return a request for comment.